Malaria parasites are unable to synthesize purines de novo and rely on the host red blood cell as a source of these materials for their growth and reproduction. The proposed program of study is designed to determine: 1. metabolic alterations taking place in the infected red cell that make purines available to the parasite, and 2. mechanisms whereby the intracellular parasite is able to accumulate purines. Studies will involve: (a) Determination of the ATP levels as well as its degradation products in normal red cells, in aged red cells and in red cells containing malaria parasites, (b) Characterization of the salvage pathway enzymes of both the red cell and the parasite, and (c) Critical studies of purine that have been removed from their host cell by use of a potent hemolytic antiserum.